How does systemd work with systemctl?

systemd is the init system and service manager used by most modern Linux distributions. systemctl is its command-line interface. Key commands: systemctl start nginx (start), systemctl stop nginx, systemctl restart nginx, systemctl reload nginx (reload config without full restart), systemctl status nginx (detailed status and recent logs), systemctl enable nginx (start on boot), systemctl disable nginx, systemctl is-active nginx (check status in scripts). View logs for a service with journalctl -u nginx -f (follow live) or journalctl -u nginx --since "1 hour ago". Service unit files live in /etc/systemd/system/ — after editing, run systemctl daemon-reload.